From bug-request at octave dot org Fri Dec 10 17:27:31 2004
Subject: (0-3*i)/inf gives NaN instead of 0
From: Schloegl Alois <alois dot schloegl at tugraz dot at>
To: bug at octave dot org
Date: Sat, 11 Dec 2004 00:21:44 +0100


Bug report for Octave 2.1.64 configured for i686-pc-linux-gnu

Description:
-----------

octave:4> version
ans = 2.1.64
octave:5> (4-3*i)/inf
ans = NaN - NaNi

The correct result is 0.

Actually, Octave 2.1.33 (on a different platform) does not seem to have this
problem.
octave:7> version
ans = 2.1.33
octave:8> (4-3*i)/inf
ans = 0



Repeat-By:
---------

  * Please replace this item with a description of the sequence of
    events that causes the problem to occur.

Fix:
---

Prof. W .Kahan mentions in his "Lecture Notes on the Status of IEEE 754" p.10
http://www.cs.berkeley.edu/~wkahan/ieee754status/IEEE754.PDF

"when (0+3i)/inf is turned naively into (0+3i)*(inf-i)/(inf^2+0^2) it generates
a NaN instead of the expected 0."



   Alois




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